Colloquia Schedule Spring 2016

"Spirals, Gaps, and Cavities: Signposts of Planets in Protoplanetary Disks?"

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Robin (Ruobing) Dong

LBNL/Berkeley

host: Adam Kraus

"The Key Influence of AGB Stars on the Evolution and Global Properties of Galaxies"

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Martha L. Boyer

NASA Goddard

host: Kristen McQuinn

"CAMPARE and Cal-Bridge: Two Synergistic Programs Forming a Successful New Model for Promoting Participation of Women and Underrepresented Minority Students in Astronomy"

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Alexander L. Rudolph

California State Polytechnic University, Pomona

host: William Cochran

"Exoplanet Atmospheres in High Resolution"

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Jayne L. Birkby

Harvard-Smithsonian Center for Astrophysics

host: Daniel Jaffe

"The Dynamical Evolution of Young Stellar Complexes in the Milky Way"

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Alison I. Sills

McMaster University, Hamilton, ON

host: Natalie Gosnell

"The Evolution of Galaxy Structural Properties"

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Rachel Somerville

Rutgers University, Downsbrough Chair in Astrophysics

host: Shardha Jogee

"A PHAT New Measurement of the High-Mass Stellar IMF"

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Daniel Weisz

UC Berkeley/University of Washington

host: Michael Boylan-Kolchin

"The Role of Dwarf-Dwarf Galaxy Interactions in Galaxy Assembly"

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Sabrina Stierwalt

NRAO/University of Virginia

host: Kristen McQuinn

No colloquium scheduled. (Spring Break)

"Exploring the z~2.3 Cosmic Web with 3D Lyman-Alpha Forest Tomography"

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Khee-Gan Lee

UC Berkeley/LBNL

host: Caitlin Casey

"Understanding Galaxy Evolution with Massive Starburst Galaxies"

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Hai Fu

University of Iowa

host: Caitlin Casey

"Implications from the Detection of the Binary Black Hole Inspiral GW150914"

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Matthew Benacquista

University of Texas Rio Grande Valley

host: J. Craig Wheeler

Stellar Seminar talk Date/Time: Wed., 12 Noon: "Title: TBA"

David Yong (Stellar Tinsley Scholar)

Mt. Stromlo Observatory, Australia

host: Fritz Benedict

"The Calm Before the Storm: Exploring the Post Accretionary Doldrums Prior to the Late Heavy Bombardment"

The early bombardment of the inner solar system played a critical role in planetary evolution, but there is still considerable uncertainty about what happened when. Dynamical models suggest two major bombardment phases may have taken place: (i) a post-accretionary period where newly-formed worlds were struck by leftover planetesimals, and (ii) a late heavy bombardment period, possibly produced by conditions related to a violent reshuffling of the planets ~4.1-4.2 Gyr ago (Ga). If valid, a relative impact lull took place between the two bombardment phases. We explore the evidence for such doldrums in this talk. Consider:

a) Mars. Geochemical and meteorite evidence indicates the giant 10,600 x 8,500 km Borealis basin formed > 4.5 Ga. Many postulated basins forming afterwards, however, can be ruled out by the surprisingly pristine nature of the Borealis boundary in topography and gravity. Three of the four largest remaining basins, Hellas, Isidis, and Argyre, have superposed craters counts indicating they are < 4.1 Ga.

b) Asteroids. The oldest and most extensive sets of 39Ar-40Ar shock degassing ages, found within meteorites that were heavily shocked, shock-melted, or otherwise showed some evidence for having been part of a large collision, show age clusters between ~3.5-4.1 Ga and ~4.4-4.54 Ga. Using dynamical/impact heating models, it can be argued that relatively few projectiles were on planet-crossing orbits between ~4.1-4.4 Ga.

c) Moon. The Moon is probably 4.47 Ga, yet most sample evidence for basin-sized impacts may be < 4.2 Ga. The age gap is curious unless many basins were created close in time to the solidification of the lunar crust. Using collisional/dynamical models, it can be shown that many early basins and craters formed > 4.4 Ga. Here the early impactors may be surviving debris from the Moon-forming giant impact event; note that ejecta initially escaping the Earth-Moon system can come back over many tens of Myr. This would leave doldrums between ~4.2-4.4 Ga.

d) Earth. Early impacts may provide the means to indirectly make Hadean-era zircons (via burial of terrains by impact-derived melt). This could mean the paucity of > 4.2 Ga zircons is not solely a survival bias, but instead are doldrums. The zircon age distribution peak near ~4.15 Ga would then tell us about the onset of the late heavy bombardment.

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William F. Bottke (Planetary Tinsley Scholar)

Southwest Research Instutite, Boulder, Colorado

host: Mike Endl/Judit Ries

"Disk Galaxy Assembly Across Cosmic Time: Combining Magnitude-limited Survey with Gravitational Lensing"

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Tiantian Yuan (Exgal Tinsley Scholar)

Australia National University

host: Chao-Ling Hung

"The Discovery and Characterization of the Y Dwarfs"

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Michael Cushing

University of Toledo

host: Brendan Bowler

"What can Binaries tell us about Planet Formation?"

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Kaitlin M. Kratter (ISM Tinsley Scholar)

Steward Observatory, University of Arizona

host: Adam Kraus